The present invention relates generally to stereophony, and in particular to four-channel stereophony using binaural signals generated from microphones mounted in dummy heads simulating the human head.
The known binaural sound recording system, is a closed circuit type of sound reproducing system in which two microphones, used to pick up the original sound, are each connected to two independent corresponding transducing channels which, in turn, are coupled to two independent corresponding earphones worn by the listener. The microphones are mounted in a dummy simulating the human head in shape and dimensions and at the locations corresponding to the ears of the human head. The listener is transferred to the location of the dummy head by means of a two-channel sound reproducing system. Because of the direct transfer of signals, the listener has spatial impressions as if sitting at the location of the dummy. However, because of the inconvenience that the listener has to wear the earphones (headphones), two-channel loudspeaker reproduction using a dummy head has been proposed to take advantage of the spatial impressions of the binaural system. However, a stereophonic pair of signals is usually reproduced by two loudspeakers standing on the right and left in front of the listener. The listener then receives at his left ear not only the wanted left signal, but an unwanted right signal as a result of sound diffraction at the head. Because of the symmetry of the system, this process is called acoustical crosstalk. This acoustical crosstalk can be eliminated by an electronic circuit as proposed by P. Damaske (Head-Related Two-Channel Stereophony with Loudspeaker Reproduction, The Journal of the Acoustical Society of America, Vol. 50 No. 4 Part II pages 1109-1115). Reproducing the binaural signals of a dummy head with two loudspeakers is still problematic in that virtual sound sources can only be produced between the two loudspeakers and in that a slight movement of the listener's head gives him an impression that the sound sources have been dislocated.